Method of producing ball valve

ABSTRACT

A ball valve includes a valve housing  10  and a ball  20.  A pair of mirror-symmetrical housing halves  12, 14  are jointed together along a single weld line to enclose the ball having a through bore and a pair of recessed portions. The through bore  22  is in conformity with the weld line. Holes  42, 50  for respectively mounting a pair of stem assemblies are formed in portions of the valve housing opposed respectively to opposite ends of the through bore. The through bore of the ball is brought into alignment with openings  12 A,  14 A of the valve housing, and the recessed portions  26, 28  of the ball are brought into alignment with the holes, respectively. Next, the pair of stem portions  60, 68  are attached to both holes and fitted into both recessed portions, and the stems are welded circumferentially to peripheral edge portions of the holes, respectively.

TECHNICAL FIELD

The present invention relates to a method of producing a ball valve tobe connected to a fluid piping system, and more particularly to a methodof assembling a housing, adapted to contain a ball therein, by welding.

BACKGROUND ART

(1) U.S. Pat. No. 4,265,427 (corresponding to JP-A-55-14394) disclosesone example ball valve which comprises, as main component members, aball, and a housing containing the ball.

In the ball valve, a spherical shut-off member (i.e. a ball), containedin a hood (or a housing), has a pair of projections (or stems), and theprojections are rotatably supported by a pair of support rings attachedto an inner surface of the hood, respectively. The hood is assembled bywelding a pair of hood halves together, and butt welding end faces ofthe pair of hood halves lie in a plane including an axis of rotation ofthe spherical shut-off member. Namely, the pair of hood halves aremirror-symmetrical with respect to the plane including the axis ofrotation of the spherical shut-off member.

The hood has an operation hole (or window) provided for rotating thespherical shut-off member around the axis, and hemi-circular recesses,corresponding to the operation hole, are formed respectively in the pairof hood halves before the two hood halves are jointed together bywelding.

The pair of support rings serve to receive a thrust force from a fluid,are provided respectively at opposed positions on the inner surface ofthe hood, and are disposed near to the axis of rotation of the sphericalshut-off member in surrounding relation thereto, wherein one of thesupport rings surrounds the operation hole. Each of the two supportrings comprises a combination of support ring halves correspondingrespectively to the pair of hood halves, and the support ring halves aresecured respectively on the inner surfaces of the pair of hood halves bywelding prior to welding of the hood halves. Therefore, when the pair ofhood halve are jointed together by welding, each pair of support ringhalves are abutted against each other at their butting end faces to formthe circular ring.

In order to prevent the inside of the hood from being affected by thewelding operation (by which the pair of hood halves are jointedtogether), a partially cut off grooved ring is attached by welding onthe inner surface adjacent to the welding face (i.e. the butt weldingend face) of one of the hood halves. The grooved ring extends toward themating hood half in the direction of the width thereof so as to extendcircumferentially along the inner side of the butted end faces of thepair of hood halves for welding.

In the ball valve having such a structure, since the pair of supportrings, which receive a thrust force from fluid, and the operation holeof the hood, are located close to the butt welded faces of the pair ofhood halves, there is a possibility that thermal strain is induced inthe hood due to welding heat resulting in a displacement of each supportring half from its proper position. In this case, the precision of theaxis of rotation of the spherical shut-off member is affected, so thatincomplete contact between valve seats, which are provided on the innersurface of the hood, and the spherical shut-off member occurs.

(2) U.S. Pat. No. 4,235,003 discloses a method of producing a ballvalve. In the disclosed ball valve, a ball is contained in a hollowmember (i.e. a housing), and the ball is rotatably supported by a pairof rings (i.e. valves seats). In the ball valve having such structure,unlike the ball valve disclosed in U.S. Pat. No. 4,265,427, the ringsreceive a thrust force from fluid.

The hollow member of the ball valve, disclosed in U.S. Pat. No.4,235,003, is formed by jointing a pair of symmetrical pipe memberstogether by welding. Each pipe member has a hemi-spherical enlargedportion (of a bowl-shape) formed at one end thereof, and open end facesof the two enlarged portions are butted and welded together at the endfaces, thereby forming the hollow member. When the ball valve is openedor closed, the ball within the hollow member is operated by an operationstem passing through a hole formed in the hollow member, the hole beingformed by a combination of hemi-circular recesses which are formedrespectively in the open ends of the two enlarged portions prior to thewelding for obtaining the hollow member. Here, the remaining portion ofeach pipe other than the enlarged portion will be referred to as astraight pipe portion, and a sleeve of a wedge-shaped cross-section forholding a ring (i.e. a valve seat) is fitted into each of the straightpipe portion, and is fixedly secured thereto by welding.

In the ball valve, although the straight pipe portions have an innerdiameter corresponding to that in a fluid piping, there is adisadvantage that the sleeves and the rings (i.e. valve seats) narrow afluid passage. Further, since the hemi-circular recesses are formedrespectively in the enlarged portions of the two pipe members prior towelding for obtaining the hollow member, there is a possibility that theoperating stem-passing hole, formed by the combination of thehemi-circular recesses, is affected by thermal strain which is inducedin the hollow member by welding, so that the center of the hole isdisplaced out of a proper position.

(3) A third example of known ball valves is shown in FIG. 5. The ballvalve comprises, as main components, a housing 01, having openings 02Aand 03A formed respectively at opposite sides thereof, a ball 05, whichis contained in the housing, and has a central through bore 05A, and apair of stems 07 and 08 supporting the ball. The ball 05 is rotated bythe operation stem 08 about the axis of the both stems. There areprovided valve seat rings 06 and 06 between the housing 01 and the ball05 which is kept always in contact with the valve seat rings 06 and 06.

The housing 01 consists of three members, that is, a first member 02, asecond member 03 and a third member 04, the first and second membersbeing mirror-symmetrical. The three members each having a generallytubular shape are butted and welded (W) at their open end faces.

The stems 07 and 08 extend through the third member 04. The stem 07extends through the third member 04 and is fixed thereto. It is alsorotatably fitted in a bore for stem of the ball 05. The other stem 08 isof an operation stem for rotating the ball valve, which rotatablyextends through the third member 04, is supported by a separate supportmember 09, and is fitted in a bore for stem of the ball 05 so as not torotate relatively to the ball.

This ball valve is of such a structure that the pair of stems 07 and 08receive a thrust force from fluid. The housing 01 is assembled byjointing the three sectional members together by welding, which isdisadvantageous from an economical point of view since the number of thecomponents is large. Besides, since the two weld lines W, W are close tothe valve seat rings 06 and 06, respectively, there will occur anunconformity with respect to the contact relationship between each ofthe valve seat rings 06, 06 and the ball 05 under the influence ofthermal strain induced in the housing. Further, since the weld lines W,W are close to the stems 07 and 08, the shape of the respective holes ofthe third member 04 for the stems is affected by the thermal strain,whereby the precision of the stems 07 and 08, that is, the axis ofrotation of the ball 05, is deteriorated, also resulting in anunconformity with respect to the contact relationship between each ofthe valve seat rings 06, 06 and the ball 05.

The present invention has been proposed under the above technicalbackground.

Problems to be solved by the invention are to reduce the number ofcomponents, in producing a so-called trunnion type ball valve, in orderto save the production cost for the trunnion type ball valve, such asthe first conventional example of U.S. Pat. No. 4,265,427 and the thirdconventional example shown in the accompanying drawing of FIG. 5, and toeliminate adverse effects of thermal strain induced in a housing due towelding whereby obtaining the ball valve with a high precision.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided the following ballvalve producing method:

a ball valve to be produced is connected to a fluid piping system, andcomprises a valve housing (for example, a wall thickness=10 to 50 mm),and a ball rotatably contained in the valve housing. The valve housingand the ball are made, for example, of carbon steel or austeniticstainless steel (JIS SUS304).

The valve housing has a pair of holes, which are located in opposedpositions so as to be connected respectively to pipes constituting thepiping system, and a pair of stem assemblies which are located inopposed positions on a straight line perpendicularly intersectinganother straight line, passing through centers of the pair of openingsand a center of the ball, at the center of the ball.

The ball has a through bore, which can be brought into alignment withthe pair of openings to allow the passage of a fluid therethrough, and apair of recessed portions receiving the pair of stem assemblies,respectively. The ball is rotatable within the valve housing about acenterline passing through the pair of stem assemblies.

The ball valve having the above structure is produced by the followingprocess:

(1) A pair of housing halves for forming the valve housing, and the ballhaving the through bore whose opposite open ends are formed to be flat,are prepared. The pair of housing halves are so formed to bemirror-symmetrical bodies of which forms are defined by sectioning thevalve housing at the middle between the pair of openings. The ball ispreviously provided with a pair of recessed portions.

(2) Annular valve seats, each forming a seal between an outer surface ofthe ball and an inner surface of the valve housing, are mounted in thepair of housing halves, respectively.

(3) The pair of housing halves are butted at their open ends (oppositeto the openings, respectively) so as to enclose the ball. At this time,the ball is kept in such a position that the ball is turned by an angleof 90 degrees from a normal operational position of the ball valve,while causing the center-line of the through bore to be in alignmentwith the operational axis of the ball and to perpendicularly intersectthe straight line passing through the centers of the pair of openingsand the center of the ball.

(4) The butted open ends of the pair of housing halves are jointedtogether by welding, thereby forming the valve housing.

(5) Without changing the position of the ball, holes for mounting thepair of stem assemblies respectively, are formed by machining at thosepositions of the valve housing faced respectively to the both flat openends of the through bore of the ball. The both holes are so formed thatthe centers thereof are located on the operational centerline of theball valve.

(6) The ball is turned by an angle of 90 degrees to be in the normaloperational state of the ball valve such that the through bore isaligned with the both holes of the valve housing and that the recessedportions of the ball are aligned with the both holes of the housing,respectively. Next, the pair of stem assemblies are attached to the bothholes, respectively, and stems are fitted into the both recessedportions, respectively, and subsequently the pair of stem assemblies arewelded circumferentially to edge portions of the holes, respectively.

An embodiment of the invention method characterized by the above stepsof the process will be described in the following:

(1) The welding at step (4) is effected by a TIG welding method (i.e.Tungsten inert-gas arc welding). In the TIG welding method, since noflux is used, spattering of slag will not occur during the weldingoperation, so that the contamination of the interior of the valvehousing by foreign matters can be effectively prevented. Here, it shouldbe noted that the entry of foreign matters, which would adversely affectthe condition of contact of the ball with the valve seats, should bepositively avoided.

(2) One of the pair of stem assemblies includes a non-operation stem,fitted in one of the two recessed portions, and an auxiliary member, anda base portion of the auxiliary member is welded circumferentially bywelding to the peripheral edge of one of the holes. The other of thepair of stem assemblies includes a sleeve, fixedly secured to the valvehousing, and a valve stem (i.e. valve-operating stem) rotatably fittedin the sleeve, with a seal ring interposed therebetween, and in acondition in which the valve stem is fitted in the sleeve, a distal endportion of the valve stem is fitted in the other recessed portion in amanner to prevent a relative rotation therebetween, and an end portionof the sleeve is jointed by welding to the peripheral edge of the holeover an entire periphery of the sleeve end portion.

(3) A flange plate is detachably fixed to a free end of the sleeve toprevent the valve stem from moving axially out of engagement with thesleeve, and a free end portion of the valve stem extends outwardly fromthe flange plate through an opening in the flange plate. Thisoutwardly-extending portion is used as a valve-operation stem forrotating the ball about the centerline of the ball to open and close theball valve.

(4) The pair of valve seats are mounted respectively on the innersurfaces of the housing halves in such a manner that the valve seats arelocated close to the pair of openings in parallel with end surfaces ofthe openings, respectively.

(5) Each of the pair of valve seats has a resilient member, and thevalve seat is brought to close contact with the outer surface of theball by a spring force of the resilient member.

(6) A body of the valve seat is a metal ring, and a resin ring ismounted on a peripheral edge of the metal ring, and the resin ring isbrought to close contact with the outer surface of the ball.

(7) A body of the valve seat is a metal ring, and a rubber ring ismounted on a peripheral edge of the metal ring, and the rubber ring isbrought to close contact with the outer surface of the ball.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a ball valve through an axisthereof, which is an intermediate product produced by the inventionmethod;

FIG. 2 is a cross-sectional view of the ball valve through the axisthereof, which is produced by the invention method;

FIG. 3 is a cross-sectional view of a part of a valve housing,explanatory of a preparatory step for forming a hole of the valvehousing after welding according to the invention method;

FIG. 4 is a cross-sectional view of a part of the valve housing,explanatory of a preparatory step subsequent to the step of forming aprovisional hole in the valve housing after welding according to theinvention method; and

FIG. 5 is a cross-sectional view of a conventional ball valve.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will now be described withreference to the drawings.

FIG. 1 shows a cross-section of a ball valve (as an intermediateproduct) through an axis thereof. FIG. 2 is a cross-sectional view ofthe assembled ball valve.

First, the structure of the ball valve will be described. A ball 20 isrotatably contained within a valve housing 10 having a generally hollowcylindrical shape. The valve housing 10 has opposite open ends (openings12A and 14A), and has a first hole 42 and a second hole 50 formedrespectively through opposed portions of a central portion of thehousing body (FIG. 1). The ball valve is connected to a piping system atthe circular openings 12A and 14A of the valve housing 10. As shown inFIG. 2, a first stem portion 60 and a second stem portion 68 are fixedlysecured respectively to the first hole 42 and the second hole 50 bywelding.

Valve Housing

The body of the valve housing 10 has such a hollow cylindrical shapethat the body is increasing in diameter from the circular openings 12Aand 14A, formed respectively at the opposite ends thereof, toward acentral portion thereof where the first hole 42 and the second hole 50,closed respectively by the first stem 60 and the second stem 50, exist.

Annular Valve Seats

A pair of annular valve seats 30 and 30 are provided on an inner surfaceof the valve housing 10 to form a seal between the valve housing 10 andthe ball 20. The ball 20 can be rotated while kept in contact with theannular valve seats 30 and 30. The annular valve seat 30 comprises ametal ring 32, serving as a base portion, a plurality of compressioncoil springs 36 (preferably, ten compression coil springs), a sealingmaterial ring 34 (For example, this is made of a resin material or arubber material), mounted on a distal end of the metal ring 32 abuttedagainst the ball 20, and an O-ring interposed between the metal ring 32and the valve housing 10. The metal ring 32 and the sealing materialring 34 are pressed against a spherical outer surface of the ball 20 bythe bias of the compression coil springs 36.

Ball

By removing portions of the ball 20, this ball is formed into such aconfiguration that parallel open ends 24 and 24 are formed respectivelyat opposite sides of the spherical body thereof, and the ball 20 has acentral through bore 22, a first recessed portion 26 and a secondrecessed portion 28 all of which are cross-sectionally circular. A keygroove is formed in the second recessed portion 28. The first recessedportion 26 and the second recessed portion 28 are formed respectively inopposite portions of the surface of the ball 20, and a straight line L1,passing through the centers of these recessed portions, perpendicularlyintersects a centerline (that is, an axis) L2 of the central throughbore 22 (FIG. 2). In the condition shown in FIG. 2, the centerline ofthe central through bore 22 is in alignment with the centerline of thevalve housing 10, that is, a straight line (i.e. the axis) passingthrough the centers of the circular openings 12A and 14A.

Stem Portions

The first stem portion 60 includes a base portion 62 (auxiliary member),and a first stem 64 (non-operating stem) in the form of a round rod. Thebase portion 62 is fitted in the first hole 42 in the valve housing 10,and is welded and fixed to a peripheral edge of the first hole. Thefirst stem 64 is fitted in the first recessed portion 26 of the ball 20.

The second stem portion 68 comprises a cylindrical sleeve 70, avalve-operating valve stem 72 (in the form of a round rod), fitted inthis sleeve so as to rotate relative thereto, and a flange plate 74secured to an outer end of the sleeve 70 by screws. One end portion ofthe sleeve 70 is fitted in the second hole 50 in the valve housing 10,and is welded and fixed to a peripheral edge of the second hole. Thevalve stem 72 projects from the one end of the sleeve 70, and is fittedin the second recessed portion 28 of the ball 20. A key 28A is engagedin key grooves, formed respectively in the valve stem 72 and the secondrecessed portion 28, thereby preventing a relative rotation between thetwo members 72 and 28. An O-ring 76 forms a seal between the valve stem72 and the sleeve 70. That portion of the valve stem 72, extendingoutwardly from the sleeve 70, is smaller in diameter than its bodyportion fitted in the sleeve 70, and this smaller-diameter portionextends through an opening, formed through the flange plate 74, and astep portion, formed between the larger-diameter portion andsmaller-diameter portion of the valve stem 72, is engaged with theflange plate 74, thereby preventing the movement of the valve stem 72 inthe axial direction. The axes of the first stem 64 and the valve stem 72lie on the straight line L1 (FIG. 2), and by rotating thesmaller-diameter portion of the valve stem 72, the ball 20 can berotated about the straight line L1 so as to open and close the ballvalve.

Next, a method of producing the ball valve will be described.

(1) Preparation of Valve Housing Constituent Members (FIG. 1):

A pair of housing halves 12 and 14 for forming the valve housing 10 areprepared. The housing halves 12 and 14 are mirror-symmetrical withrespect to a plane (reference plane) including the common axis of thefirst and second holes 42 and 50, formed in the valve housing 10, andthe center C of the ball. The housing half 12 are open at its oppositeends, and has the opening 12A and a larger-diameter end 12B. Similarly,the housing half 14 has the opening 14A and a larger-diameter end 14B.The annular valve seats 30 are mounted in the housing halves 12 and 14,respectively. This mounting relation will be described with respect tothe housing half 12, and a step portion is formed on that portion of theinner surface of the housing half 12, disposed near to the opening 12Aof the housing half 12, in parallel relation to this opening 12Adefining a flat opening lying in a plane, and the annular valve seat 30is inserted into the housing half 12 through the larger-diameter end12B, and is mounted on this step portion in fitted relation thereto.Similarly, the annular valve seat 30 is mounted on the housing half 14.As described above, each of the annular valve seats 30 and 30 serves toform a seal between the outer surface of the ball and the inner surfaceof the valve housing.

(2) Preparation of Ball (FIG. 1):

There is prepared the ball 20 which includes the central through bore 22for allowing the flow of a fluid, and the opposite open ends 24 and 24which are flat and parallel to each other. The first recessed portion 26and the second recessed portion 28 are preformed in the ball 20 bymachining. These recessed portions lie on the common axis.

(3) Combination of Housing Halves with Ball:

The housing halves 12 and 14 are butted at their open ends 12B and 14B(opposite with respect to the openings 12A and 14A, respectively) in amanner to enclose the ball 20. At this time, the ball 20 is kept in sucha position that the direction of the ball 20 is turned by an angle of 90degrees with respect to a normal ball valve operational condition, withthe centerline of the through bore 22 coinciding with the centerline ofthe ball 20 (about which the ball is opened and closed), andperpendicularly intersecting the straight line passing through thecenters of the openings 12A and 14A and the center of the ball 20.

(4) Welding:

The butted open ends (larger-diameter ends) 12B and 14B of the housinghalves 12 and 14 are jointed together by welding (W), thereby formingthe valve housing 10. This welding is effected by a TIG welding method.With this TIG welding, slag will not be scattered over the interior ofthe valve housing 10 during the welding, and this can serve to ensurethe performance of the ball valve. In a preferred practical method,first to third layers of weld beads are formed by TIG welding, andsubsequent bead layers are formed by an MIG welding method (Inert gasarc welding using a consumable electrode) or a submerged arc method.

(5) Formation of Holes:

While keeping the ball 20 in the position described in the above Item 3,the pair of holes (the first hole 42 and the second hole 50) forrespectively mounting the stem portions 60 and 68 are formed bymachining respectively in those portions of the valve housing opposedrespectively to the flat open ends 24 and 24 of the through bore 22. Atthis time, the centers of the two holes to be formed lie on theoperational centerline of the ball valve about which the ball is openedand closed.

Specifically, the holes are formed according to the following procedure(see FIGS. 3 and 4).

FIG. 1 shows a condition in which the first hole 42 and the second hole50 are already formed, but description will start from the condition inwhich the valve housing is as welded, and the holes are not yet formed.The two holes are formed by the same method, and therefore only themethod of forming the first hole 42 will be described, and descriptionof the method of forming the second hole 50 will be omitted.

a. That portion, corresponding to the first hole 42, is cut to be formedinto a flat surface 40, as shown in FIG. 3.

b. Screw holes 44 and 44 are formed respectively in positions which arepoint-symmetrical with respect to the imaginary center of the first hole42 disposed on the weld line W, and screws, each having a hook, arethreaded into the screw holes 44 and 44, respectively.

c. An annular groove 46 is formed in surrounding relation to the screwholes 44 and 44, and is spaced outwardly from these screw holes. Thedepth of the annular groove 46 is slightly smaller than the wallthickness of the relevant portion, and the remaining wall thickness is aminimum dimension which can support the weight of a disk portion definedby the annular groove 46.

d. The disk portion, formed inside the annular groove 46, is pulled hardoutwardly, using the pair of screws (each having the hook) threadedrespectively in the screw holes 44 and 44, thereby rupturing the thinwall portion remaining at the bottom of the annular groove 46. As aresult of this operation, a provisional hole 48 is formed (FIG. 4).

e. Utilizing the thus formed provisional hole 48, an annular foamedresin 52 is interposed between the open end 24 of the through bore ofthe ball 20 and the inner surface of the valve housing 10.

f. A peripheral edge portion of the provisional hole 48 is removed bycutting, thereby forming the first hole 42 (see broken lines in FIG. 4)of the predetermined size. At this time, because of existence of theannular foamed resin 52, cuttings, produced when cutting the peripheraledge portion of the provisional hole 48, will not enter spaces in whichthe spherical surface portions of the ball 20 are disposed,respectively. Incidentally, if the above steps a to e are effected forthe second hole 50 before the peripheral edge portion of the provisionalhole 48 is removed by cutting, the influence of the cuttings on thespherical surface portions of the ball 20 can be prevented morepositively. After the peripheral edge portion of the provisional hole 48is removed by cutting, the inner surface of the through bore 22 iscleaned, and the annular foamed resin 52 is removed.

(6) Welding of Stem Portions

After the operations of the above five Items are finished, the ball 20is turned by an angle of 90 degrees, and is brought into the positionshown in FIG. 2. In this ball position, the first stem portion 60 andthe second stem portion 68 are disposed in alignment with the first hole42 and the second hole 50, respectively.

a. First Stem portion 60: The base portion 62 and the first stem 64 areinserted into the first hole 42 and the first recessed portion 26,respectively. The base portion 62 is larger in diameter than the stem64. The peripheral surface of the base portion 62 is jointed to theperipheral edge portion of the first hole 42 by TIG welding (W).

b. Second Stem portion 68: The valve stem 72 and the sleeve 70 arepreviously assembled together. The distal end portion of the valve stem72, projecting from the sleeve 70, is inserted into the second recessedportion 28. At this time, the key 28A is engaged in the key groove,formed in the second recessed portion 28, and the key groove formed inthe valve stem 72, to prevent the valve stem 72 from rotating in thesecond recessed portion 28. Subsequently, while the valve stem 72 ismounted in the second recessed portion 28, the outer surface of thesleeve 70 is jointed to the peripheral edge portion of the second hole50 by TIG welding (W). By effecting the welding in the mounted conditionof the valve stem 72, the alignment of the sleeve 70 at the time of thewelding can be effected accurately.

When the welding of the stems is effected, the assemblage of the ballvalve 10 is completed. Thereafter, pipes of the fluid piping system areconnected respectively to the openings 12A and 14A of the ball valve 10.

Advantages of the present invention are as follows:

(1) In the present invention, the valve housing is formed by welding thepair of housing halves together, and the number of the component partsare smaller as compared with the conventional trunnion-type ball valve(shown in FIG. 5) in which the valve housing is formed by the threehousing members. And besides, the welding portion, required forassembling the valve housing, is one, and therefore the production costcan be reduced.

(2) The weld line, formed at the time of assembling the valve housing,can be disposed at the central position of the valve housingsufficiently spaced from the valve seats, and therefore the influence ofthe welding heat on the valve seats is small, and this can contribute tothe enhanced precision of the ball valve.

(3) The pair of holes for respectively mounting the stem assemblies areformed after the housing halves are jointed together by welding, andtherefore in contrast with the case where the holes are previouslyformed, and therefore the holes are not subjected to the influence ofthermal strain due to the welding, so that the axes of the stems can beset highly precisely.

(4) When forming the pair of holes after the valve housing is assembledby jointing the housing halves together by welding, the opposite openends of the through bore of the ball (which is rotatable within thevalve housing) are disposed in alignment with the pair of holes,respectively, and by doing so, the influence of cuttings, formed at thetime of formation of the holes, on the spherical surface of the ball andthe valve seats, can be prevented. And, after the holes are formed, theball can be returned into the normally-used condition by rotating thisball by the angle of 90 degrees, and therefore this is convenient.

(5) In the ball valve formed in accordance with the present invention,the valve seats are previously mounted within the housing halves,respectively, and the ball is received, and the valve housing isassembled (by welding), and therefore in contrast with the ball valve,disclosed in U.S. Pat. No. 4,235,003 (in which the valve housing isassembled after putting a ball in the housing, thereafter the valveseats are inserted and fixed to the valve housing by welding), thethrough bore of the ball is sufficiently large, and can be formed intothe same diameter as the diameter of the fluid inlet and outlet openingsin the valve housing, and the ball valve will not offer a resistance tothe flow of the fluid (that is, will not disturb a stream line of thefluid flow).

Capability of Exploitation in Industry

The method of the present invention can be applied to both small-sizeand large-size ball valves, and is suited particularly for theproduction of a large-size ball valve incorporated in a pipeline forpetroleum or natural gas.

What is claimed is:
 1. A method of producing a ball valve which isadapted to be connected to a fluid piping system, and comprises a valvehousing, and a ball rotatably contained in the valve housing, whereinthe valve housing has a pair of openings, which are located in opposedpositions so as to be connected respectively to pipes constituting thepiping system, and a pair of stem assemblies which are located inopposed positions on a straight line perpendicularly intersectinganother straight line, passing through centers of the pair of openingsand a center of the ball; and wherein the ball has a through bore, whichcan be brought into alignment with the pair of openings to allow thepassage of a fluid therethrough, and a pair of recessed portionsreceiving the pair of stem assemblies, respectively, and the ball isrotatable within the valve housing about a centerline passing throughthe pair of stem assemblies, characterized in that: a pair of housinghalves for forming the valve housing, and the ball having the throughbore whose opposite open ends are formed to be flat, are prepared, thepair of housing halves being so formed to be mirror-symmetrical bodiesof which forms are defined by sectioning the valve housing at the middlebetween the pair of openings, and the ball being previously providedwith a pair of recessed portions; annular valve seats, each forming aseal between an outer surface of the ball and an inner surface of thevalve housing, are mounted on the pair of housing halves, respectively;the pair of housing halves are butted at their open ends, which areopposite to the openings, respectively, so as to enclose the ball, onthe other hand, the ball is kept in such a position that the ball isturned by an angle of 90 degrees from a normal operational position ofthe ball valve, while causing the centerline of the through bore to bein alignment with an operational axis of the ball and to perpendicularlyintersect the straight line passing through the centers of the pair ofopenings and the center of the ball; the butted open ends of the pair ofhousing halves are jointed together by welding, thereby forming thevalve housing; subsequently, without changing the position of the ball,holes for mounting the pair of stem assemblies respectively, are formedby machining at those positions of the valve housing faced respectivelyto the both flat open ends of the through bore of the ball so that thecenters thereof are located on the operational centerline of the ballvalve; and the ball is turned by an angle of 90 degrees to be in thenormal operational state of the ball valve such that the through bore isaligned with the both openings of the valve housing and that therecessed portions of the ball are aligned with the both holes of thehousing, respectively, next, the pair of stem assemblies are attached tothe both holes, respectively, and stems are fitted into the bothrecessed portions, respectively, and subsequently the pair of stemassemblies are welded circumferentially to edge portions of the holes,respectively.
 2. A ball valve-producing method according to claim 1,wherein the step of jointing the open ends of the pair of housing halvestogether by welding is effected by a TIG welding method.
 3. A ballvalve-producing method according to claim 1, wherein one of the pair ofstem assemblies has a non-operation stem, which is fitted in one of therecessed portions, and an auxiliary member, and a base portion of theauxiliary member is welded circumferentially by welding to theperipheral edge of one of the holes; and the other of the pair of stemassemblies includes a sleeve, which is fixedly secured to the valvehousing, and a valve stem rotatably fitted in the sleeve, with a sealring interposed therebetween, and a distal end portion of the valve stemis fitted in the other recessed portion so as not to relatively rotatewhile the valve stem is fitted in the sleeve, and an end portion of thesleeve is welded circumferentially to the peripheral edge of the hole.4. A ball valve-producing method according to claim 1, wherein a flangeplate is detachably fixed to a free end of the sleeve to prevent thevalve stem from moving axially out of engagement with the sleeve, a freeend portion of the valve stem extends outwardly from the flange platethrough an opening of the flange plate, and the outwardly-extendingportion is used as a valve-operation stem for rotating the ball aboutthe operational centerline of the ball to open and close the ball valve.5. A ball valve-producing method according to claim 1, wherein the pairof valve seats are mounted respectively on the inner surfaces of thehousing halves in such a manner that the valve seats are located closeto the pair of openings in parallel with end surfaces of the openings,respectively.
 6. A ball valve-producing method according to claim 1,wherein each of the pair of valve seats has a resilient member, and thevalve seat is brought to close contact with the outer surface of theball by a spring force of the resilient member.
 7. A ballvalve-producing method according to claim 6, wherein a body of the valveseat is a metal ring, and a resin ring is mounted on a peripheral edgeof the metal ring, and the resin ring is brought to close contact withthe outer surface of the ball.
 8. A ball valve-producing methodaccording to claim 6, wherein a body of the valve seat is a metal ring,and a rubber ring is mounted on a peripheral edge of the metal ring, andthe rubber ring is brought to close contact with the outer surface ofthe ball.